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Point Of Impact Adjustment


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#1 beechnut

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Posted 25 January 2004 - 08:28 AM

Are there different height front sights available? I installed a NOS lyman sight on my 1928 WH, and my point of aim is pretty high. With the tanget sight I'm hitting about 8-10" at 20yds. With the aperture at lowest setting, my impact is about 12" high at 20yds.


I'm starting to think I should have lapped the Lyman sight base to adjust for this. I have no Idea how I would have known how far to go. Now, the easiest anser seems to be installing a taller front sight. I don't recall seeing any number stamped on my front sight, but I never took it out of the Cutts comp. And since the TSMG parts graveyards never list different sizes I may be on my own. That leaves me with TIGing up a bead on the blade, and filing down for correct elevation.


Any suggestions?
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#2 Hurridale

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Posted 25 January 2004 - 10:05 AM

Well, I'm no gunsmith, but here are some thoughts:

From what I figure, you would have to raise that front sight post about 0.237" to get it to shoot at a point of aim 8" lower at 20 yards, and .356" for 12". That makes for a REALLY high front sight post! How did it shoot before the Lyman?

I checked my Savage M1928A1 and my Colt 1921 AC. Both have a front sight which measures .720 high, measured from the top of the barrel. The Lymans appear to be identical, but when I measured the height of the tangent sight in the folded down position, the Savage measured .640" and the Colt .610". The thicknesses of the base of the Lymans are the same, as are the heights of the adjustable sight block.

What IS different is the height of the block that the sight folds down upon. It is a good .025" higher on the Savage (.115" v. .087"). I would not have noticed if I hadn't gotten out the caliper, trying to figure out your problem. Of course, this would not make any difference when firing through the aperature sight when raised.

I can't comment on which shoots where. I don't have numbers for how high they shoot, but they do seem to both shoot high from the aperature at short ranges. Sounds like a good excuse to go to the range.

I did have a problem shooting high with the Savage for a while (I shoot it much more often). I tried some unjacketed lead bullets, and they fouled the bottom of the compensator so badly that they built a ramp which was apparently pushing up the rounds. I had to take the comp off to scrape it all out. Accuracy improved immediately.

So for suggestions (worth what you're paying for them): check for lead fouling in the comp, then measure the heights described to help pinpoint the problem.

I hope this helps.

Regards,
DC
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#3 Bisley45

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Posted 25 January 2004 - 10:07 AM

to adjust elevation you raise rear sight or lower your front sight. No need to tig just file your front sight down until the bullets hit the black.

BB
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#4 Hurridale

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Posted 25 January 2004 - 10:39 AM

BB,

Isn't that backward? To lower the point of impact, shouldn't he RAISE his front sight, thereby depressing the gun?

Regards,
DC
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#5 bug

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Posted 25 January 2004 - 10:45 AM

Hurridale's numbers are about the same as mine. Since lowering the rear sight is probably not an option you must raise the front sight. I would measure it and then build it up by about 0.3" using a good epoxy. Test fire/file until you are satisfied. See what the final sight height is and either get a replacement sight that is high enough or build up the top of the old one with weld and file to the correct height.

This all assumes that you have tried more than one type of ammo, that the bore and compensator are clear and not impacting trajectory in any way.

Goog luck.
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#6 PK.

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Posted 26 January 2004 - 09:18 AM

I have noticed different height front sights. While there are smaller variances within categories, two different heights stand out and could be called “tall and short”; you wouldn’t have any trouble telling them apart.

In general, the tall sight is the one you want (sounds like you have a short) and it is much more prevalent. The current sight offered by Kahr is well made (believe it or not) and one of the tallest- a good candidate for you to try.

Keep this in mind, the “battle sight” setting on the Lyman (leaf folded down, small notch visible) is intended to allow hits on a torso out to 200 yards (or something like that, no time now to look it up), so it will hit high at the ranges we normally use these guns. With the staff up and the aperture set to a specific distance, the POI should correspond with the marking on the staff.

In my opinion, 20 yards is to close to make any judgment, adjust your front sight to get it on at 50 yd. with the staff up and the slide at ‘0’ and you should be quite satisfied.

Also, the open bolt will cause poi to shift dependent on the support given to the gun while firing. It will be quite different fired from sandbags or sitting or standing. Before you set anything in stone, try all positions and note the differences in POI, then decide how you will likely use the gun and proceed accordingly.

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#7 giantpanda4

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Posted 26 January 2004 - 03:44 PM

PK is definitely right about the POI change!
I shoot left-handed, and I always hit way to the right edge of the targets when a gun is sighted in for a right hander.
Same goes with sandbags - I suggest sighting it in from the same position as you will be shooting, if you can.
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